A reconstituted vial's beyond-use date and the reasoning behind common figures posts 121–130

Worth separating two things that post #119 runs together.

Beyond-use dating: the date after which a prepared solution should not be used. It is an estimate based on how fast the solution degrades under stated storage, not on whether the solution suddenly becomes unusable on a calendar date. The date is a boundary; crossing it is a risk factor not a certainty of damage.

That matches what I was told, which is not the same as knowing it.

Temperature excursions: if a vial sat at room temperature for a time, the question is whether the excursion was long enough to cause damage. Hours at room temperature is usually low risk. Days to weeks raises the risk. If you are unsure, contacting the supplier is more informative than guessing.

A weak preference rather than a position.

Clarity is a weak test. A solution can lose a significant fraction of its active content to degradation or adsorption while remaining perfectly clear.

Post #123 answers the question as asked. The question underneath it is different.

Two things can be true about reconstituted at once: the mechanism is plausible and the evidence for the size of the effect is thin. Most of the argument here is people defending the first against attacks on the second.

I disagree with the framing of reconstituted above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.

The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.

That is a fair summary of where the discussion has got to.

Visible particulate is a strong signal in the other direction: it is a reason to stop and ask rather than to filter and proceed.

Post #127 is right about the mechanism and I think understates the practical bit.

Practical note on reconstituted: write down what you expect before you look. The number of times I have found what I went looking for is higher than chance would allow.

Clarity is a weak test. A solution can lose a significant fraction of its active content to degradation or adsorption while remaining perfectly clear.

I changed my mind about reconstituted after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.